This invention relates to control of an infinite speed for vehicles.
Tokkai Hei 9-42428 published by the Japanese Patent Office in 1997 discloses an infinite speed ratio transmission (hereinafter referred to as IVT) wherein a reduction gear (fixed speed ratio transmission) and a planetary gear set are combined with a continuously variable transmission (CVT), in order to further enlarge the speed ratio range of a toroidal continuously variable transmission for vehicles.
In this IVT, the CVT and reduction gear are connected to the input shaft driven by an engine, the output shaft of the CVT is joined to a sun gear of the planetary gear set, and the output shaft of the reduction gear is joined to a planet carrier of the planetary gear set via a power recirculation clutch. A ring gear of the planetary gear set is joined to the final output shaft of the IVT which drives the drive wheels. The output shaft of the CVT is also joined to this final output shaft via a direct clutch.
In a direct mode wherein the direct clutch is engaged and the power recirculation clutch is disengaged, the rotation of the output shaft of the CVT is directly output to the final output shaft. In the power recirculation mode wherein the direct clutch is disengaged and the power recirculation clutch is engaged, the rotation direction and speed of the final output shaft vary according to the difference of the rotation speed of the output shaft of CVT, and the rotation speed of the output shaft of the reduction gear. Since the speed ratio of the reduction gear is constant, in the power recirculation mode, the vehicle is advanced and reversed only by varying the speed ratio of the CVT without changing the rotation direction of the input shaft. The change-over of the power recirculation mode and direct mode is performed at a rotation synchronization point RSP at which the output rotation speed of the IVT in both modes is equal.
In the power recirculation mode, the rotation of the final output shaft stops at the boundary between advance and reverse. As the rotation of the input shaft is continued even in this case, the speed ratio of the IVT becomes infinite. This boundary point is referred to as the geared neutral point GNP. If the speed ratio of the CVT is increased from the GNP, the vehicle is advanced, and if it reduced from the GNP the vehicle is reversed.
The speed ratio of CVT is varied by the gyration angle of power rollers which transmit rotational torque in the CVT. More specifically, trunnions which support the power rollers are driven by oil pressure actuators to vary the gyration angle. A reaction force to the transmitted rotational torque acts on the power rollers, and the oil pressure actuators support this reaction force. Therefore, the transmission torque of the power rollers can be controlled by controlling the pressure applied to the pistons of the oil pressure actuators. Control of the speed ratio of the CVT, control of the transmission torque, and the engaging and disengaging of the direct clutch and power recirculation clutch are performed by signals output from a control unit.
When the vehicle is advancing or reversing, the speed ratio of the IVT approaches the geared neutral point GNP as the vehicle speed decreases.
At that time, if an IVT speed ratio exceeding the GNP is commanded due to a failure or malfunction of the control unit, a torque in the reverse direction to the running direction of the vehicle will act on the final output shaft, and excessive braking will occur as a result.
Tokkai Hei 10-325459 published by the Japanese Patent Office in 1998 discloses separation of actuators and control valves which are used for the control of the speed ratio of the CVT depending on the direction of vehicle motion. In other words, the actuator and control valve to apply are changed according to whether the speed ratio of the CVT is larger or smaller than the GNP.
The control of the CVT speed ratio is performed not only in the power recirculation mode but also in the direct mode. In the direct mode, the final output shaft rotates in the forward direction regardless of the CVT speed ratio. In other words, in the direct mode, forward travel is performed also in the region where the CVT speed ratio is smaller than the GNP. However, in this IVT, when the CVT speed ratio is smaller than the GNP equivalent value, an advance actuator and control valve cannot be used. As a result, in the direct mode, a CVT speed ratio smaller than the GNP equivalent value cannot be used, and the usable range of the IVT speed ratio becomes narrow. Further, if separate actuators and separate control valves are provided for advancing and reversing, the construction and control process of the control unit are complicated and this increases the cost of the control device.
It is therefore an object of this invention to prevent the IVT from exerting a torque on the drive wheels in an opposite direction to the running direction of the vehicle without narrowing the usable range of the speed ratio.
In order to achieve the above object, this invention provides a speed change controller for such an infinite speed ratio transmission for a vehicle that comprises an input shaft, a continuously variable transmission which comprises a first output shaft and transmits a rotation of the input shaft at an arbitrary speed ratio to the first output shaft, a fixed speed ratio transmission which comprises a second output shaft and transmits the rotation of the input shaft at an arbitrary speed ratio to the second output shaft, a planetary gear set comprising a first rotation element joined to the first output shaft, a second rotation element joined to the second output shaft, and a third rotation element which varies a rotation direction and a rotation speed according to a difference between a rotation speed of the first rotation element and a rotation speed of the second rotation eliminating a selector lever which selects an operating range of the infinite speed ratio transmission.
The vehicle runs according to the rotation of the third rotation element and the operating range comprises a forward motion range and a reverse motion range.
The controller comprises an actuator which varies an amount of torque transmitted between the input shaft and the second output shaft, a sensor which detects the operating range selected by the selector lever, and a mechanism which controls the actuator according to the operating range so that a rotation torque in an opposite direction to a vehicle travel direction represented by the operating range is not transmitted between the input shaft and the first output shaft.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.